Young people between the ages of 12 and 27, especially young women, are engaging in sexual activity at an earlier age, and their attitudes toward sex are becoming more liberal, a report concludes.

Between 1943 and 1999, the average age of first intercourse among young women dropped from 19 to 15, and the number of sexually active girls increased from 13 percent to 47 percent. Approval of premarital sex also increased during that time, from 12 percent to 73 percent among young women, and from 40 percent to 79 percent among young men.

The report, published in the September issue of the Review of General Psychology, is based on an analysis of data from 530 studies, which included more than 250,000 young people over the course of five decades.